Marsh headphone amp from Linear Audio

Soldering a parallel resistor is tiresome.

Yes, and ugly too :p You can simply attach a trimpot, fine-tune, and replace it with a fixed resistor. This is how I did it, and it turned out quite easy to do. You don't even have to solder/desolder it: chose a piece of cable that tightly fits in the hole

(And you don't need to do it for both resistors. Either R9 or R10 will do).
 

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It's simple -- Nelson used them in various First Watt designs -- they are inexpensive (availble from Digikey) and compare quite favorably measurement-wise with the more expensive variety. I claim no prize for originality.

Thanks for the comment Jack....I think I´ll use precision metal film since I have them handy, next time I order some components will include some metal oxide ones and give them a try.
 
Just a general comment, I have had some problems getting the 2N5457 Jfet.
Mouser only have large quantity for sale and RS no longer stock them. I have found this little supplier who will do matched pairs or quads at a "reasonable" price and a very reasonable postage of just £1.95. They also have some good priced chrome LED mounts too.
http://stompville.co.uk/shop/
No not as cheap as can be got from the trade suppliers but then 2500 JFets is a bit over the top just to match a pair or two up. :)
Martin
 
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Can any pls give me some advise,
The heatsinks CafeNoir suggests are Aavid 581002B02500G these are 17.4 K/W from Mouser however I can get some ML26AAG heatsink RS No712-4206 from RS but these are 17.9K/W will they be ok or should I go for a more efficient heatsink?
I will be able to mount these vertically not horizontally as they suggest in the data sheet.
How hot does this amp get I will be putting in an enclosure which may not be vented.... not sure yet have to see what is available
any advice appreciated
Martin.
 
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Can any pls give me some advise,
The heatsinks CafeNoir suggests are Aavid 581002B02500G these are 17.4 K/W from Mouser however I can get some ML26AAG heatsink RS No712-4206 from RS but these are 17.9K/W will they be ok or should I go for a more efficient heatsink?
I will be able to mount these vertically not horizontally as they suggest in the data sheet.
How hot does this amp get I will be putting in an enclosure which may not be vented.... not sure yet have to see what is available
any advice appreciated
Martin.

OOOps,
Forget that last post I have just re read these posts and found the answer :eek:
But now I am on the way to sorting out the bits any guidance or thoughts on volume pots/attens would be helpfull. Alps Blue shunted a la World Desgns forum or ladder atten from FleaBay?
Regards Martin
 
Indeed.
I am surprised I haven't seen anyone's comments yet about their experiences with AutoEQ yet.

and by the way Dick, thanks for this project and the many others you've published over published the years. I made the bulk of my living with almost 30 years in telecomm electronics. audio/electronic music has been a fun hobby for me since the third grade and I am excited to have a 4.5 year old grandson who is absolutely fascinated by my oscilloscopes. i am sure he will get the bug early!
:D
mlloyd1

It will be good to hear about some completions and listen to your music soon.
Thx-Richard Marsh
 
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Joined 2012
AutoEQ is pretty amazing. I havent published a lot but I only do so when I feel I have something significant to offer and teach at the same time. I too got the bug at an early age... started with one of those 100 in 1 electronic experimenters kits. I put it on top of the cloths drier and I stood there for hours making different circuits and learning what they did.

I love the arts and music in particular all my life... audio has make a wonderful hobby as well as an added learning experience. There are so many aspects to it and the technologies - as everywhere - keep changing which keeps it interesting.

-Dick Marsh
 
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I too got the bug at an early age... started with one of those 100 in 1 electronic experimenters kits.

My dad got me the Knight 100:1 kit for Christmas when I was in 6th grade. I still have remnants and keep one of the germanium rectifiers taped to my workbench as a reminder. (I also had the Knight AM broadcast transmitter -- which now goes for over $100 on EBay!)
 
?? awfully quiet out there... .
I just found this thread. Your circuit reminds me of a update that you sent to me (delivered by....a mail carrier!!!) in 1981 of your Passive EQ preamp line stage. Good ideas never die! That line stage later got modified with more of your refinements that appeared in TAA in the mid 80's. Yes, I built that variant as well. Anyone on the fence about building this circuit should order the parts now before word gets out and Mouser- DigiKey raises their prices.

-T